Single molecule tracking of bacterial cell surface cytochromes reveals dynamics that impact long-distance electron transport.

Using a series of multiheme cytochromes, the metal-reducing bacterium Shewanella oneidensis MR-1 can perform extracellular electron transfer (EET) to respire redox-active surfaces, including minerals and electrodes outside the cell. While the role of multiheme cytochromes in transporting electrons across the cell wall is well established, these cytochromes were also recently found to facilitate long-distance (micrometer-scale) redox conduction along outer membranes and across multiple cells bridging electrodes. Recent studies proposed that long-distance conduction arises from the interplay of electron hopping and cytochrome diffusion, which allows collisions and electron exchange between cytochromes along membranes.

A bacterial membrane sculpting protein with BAR domain-like activity.

Bin/Amphiphysin/RVS (BAR) domain proteins belong to a superfamily of coiled-coil proteins influencing membrane curvature in eukaryotes and are associated with vesicle biogenesis, vesicle-mediated protein trafficking, and intracellular signaling. Here, we report a bacterial protein with BAR domain-like activity, BdpA, from MR-1, known to produce redox-active membrane vesicles and micrometer-scale outer membrane extensions (OMEs). BdpA is required for uniform size distribution of membrane vesicles and influences scaffolding of OMEs into a consistent diameter and curvature.

In situ imaging of bacterial outer membrane projections and associated protein complexes using electron cryo-tomography.

The ability to produce outer membrane projections in the form of tubular membrane extensions (MEs) and membrane vesicles (MVs) is a widespread phenomenon among diderm bacteria. Despite this, our knowledge of the ultrastructure of these extensions and their associated protein complexes remains limited. Here, we surveyed the ultrastructure and formation of MEs and MVs, and their associated protein complexes, in tens of thousands of electron cryo-tomograms of ~90 bacterial species that we have collected for various projects over the past 15 years (Jensen lab database), in addition to data generated in the Briegel lab.

Roadmap on emerging concepts in the physical biology of bacterial biofilms: from surface sensing to community formation.

Bacterial biofilms are communities of bacteria that exist as aggregates that can adhere to surfaces or be free-standing. This complex, social mode of cellular organization is fundamental to the physiology of microbes and often exhibits surprising behavior. Bacterial biofilms are more than the sum of their parts: single-cell behavior has a complex relation to collective community behavior, in a manner perhaps cognate to the complex relation between atomic physics and condensed matter physics.

Extracellular Multiheme Cytochrome PgcA Facilitates Respiration to Fe(III) Oxides But Not Electrodes.

Extracellular cytochromes are hypothesized to facilitate the final steps of electron transfer between the outer membrane of the metal-reducing bacterium and solid-phase electron acceptors such as metal oxides and electrode surfaces during the course of respiration. The triheme -type cytochrome PgcA exists in the extracellular space of , and is one of many multiheme -type cytochromes known to be loosely bound to the bacterial outer surface. Deletion of using a markerless method resulted in mutants unable to transfer electrons to Fe(III) and Mn(IV) oxides; yet the same mutants maintained the ability to respire to electrode surfaces and soluble Fe(III) citrate.

Reduction of low potential electron acceptors requires the CbcL inner membrane cytochrome of Geobacter sulfurreducens.

The respiration of metals by the bacterium Geobacter sulfurreducens requires electrons generated by metabolism to pass from the interior of the cell to electron acceptors beyond the cell membranes. The G. sulfurreducens inner membrane multiheme c-type cytochrome ImcH is required for respiration to extracellular electron acceptors with redox potentials greater than -0.

Scarless Genome Editing and Stable Inducible Expression Vectors for Geobacter sulfurreducens.

Metal reduction by members of the Geobacteraceae is encoded by multiple gene clusters, and the study of extracellular electron transfer often requires biofilm development on surfaces. Genetic tools that utilize polar antibiotic cassette insertions limit mutant construction and complementation. In addition, unstable plasmids create metabolic burdens that slow growth, and the presence of antibiotics such as kanamycin can interfere with the rate and extent of Geobacter biofilm growth.

Homeostatic adaptations in brain energy metabolism in mouse models of Huntington disease.

Impairment of energy metabolism is a key feature of Huntington disease (HD). Recently, we reported longitudinal neurochemical changes in R6/2 mice measured by in-vivo proton magnetic resonance spectroscopy ((1)H MRS; Zacharoff et al, 2012). Here, we present similar (1)H MRS measurements at an early stage in the milder Q111 mouse model.

Cortical metabolites as biomarkers in the R6/2 model of Huntington's disease.

To improve the ability to move from preclinical trials in mouse models of Huntington's disease (HD) to clinical trials in humans, biomarkers are needed that can track similar aspects of disease progression across species. Brain metabolites, detectable by magnetic resonance spectroscopy (MRS), have been suggested as potential biomarkers in HD. In this study, the R6/2 transgenic mouse model of HD was used to investigate the relative sensitivity of the metabolite profiling and the brain volumetry to anticipate the disease progression.